The overall objective of the research proposed in this application is to characterize the inorganic anion permeability pathways in the Ehrlich ascites tumor cell. The kinetic characteristics of chloride, sulfate and inorganic phosphate transport across the plasma membrane of this cell suggests that in order for these anions to enter the cell they must first interact with specific membrane carrier systems. Our previous studies have provided evidence consistent with the view that chloride and sulfate utilize a single carrier possessing two reactive sites while inorganic phosphate utilizes an entirely separate system. The existence of two annion recognition sites on the anion transporter is also suggested by our observation that C1- at concentrations greater than 60 mM can inhibit its own transport. In addition to this finding recent studies from this and other laboratories have shown that C1- may use three different transport pathways: non-mediated diffusion, co-transport with K+ and possibly Na+, and mediated self exchange through the anion transporter. The experiments proposed in this application are designed to quantitatively evaluate the contribution of each oc these permeability pathways. The kinetic characteristics of self-inhibition will be studied by investigating the effects of NO3- and the halides on C1- transport. The results of these studies will enhance our understanding of the factors involved in the regulation of C1- transport in tumor cells and hopefully provide additional insights into the nature of the anion recognition sites. Phosphate transport is apparently mediated by a carrier that is separate and discrete from that used by either chloride or sulfate. We have recently observed that phosphate transport is dependent, to a large extent, on the extracellular sodium concentration. Consequently, it is possible that a sodium-phosphate co-transport system exists. We plan to examine this possibility by investigating the kinetic profile of sodium-phosphate interaction, and therby lay the foundation for establishing the source(s) of energy for phosphate transport.